Research

Functions of the thalamus in perception and cognition

The pulvinar is the largest nucleus in the primate thalamus and is considered a higher-order thalamic nucleus because it forms input-output loops almost exclusively with the cortex. From an anatomical perspective, the pulvinar is ideally positioned to regulate the transmission of information to the cortex and between cortical areas to influence perceptual and cognitive processes. However, experimental evidence in support of such a functional role has been sparse. The most compelling evidence for the pulvinar playing an important role in visual perception and cognition has come from lesion studies in humans and monkeys. These studies point to the critical involvement of the pulvinar in a number of fundamental cognitive functions, including orienting responses and the exploration of visual space, feature binding, and the filtering of unwanted information. The underlying neural correlates of these cognitive operations in the pulvinar are largely unclear. One of the lab's major objectives is to define the role of the pulvinar in visual attention using an integrated multi-modal methods approach that includes fMRI, dMRI, electrophysiology, and behavioral measures.


Attention network dynamics

The visual environment contains more information than can be processed simultaneously. Due to this limited processing capacity of the visual system, it is necessary to select the behaviorally most relevant information for further processing and to filter out the unwanted information, a fundamental ability known as attentional selection. There is converging evidence from physiology studies in monkeys and neuroimaging studies in humans that attentional selection occurs at multiple stages along the visual pathway. For example, neural responses are modulated by spatially directed attention to a target location as early as in the thalamus and at each successive cortical processing stage as well. These modulatory influences appear to be generated by a network of higher-order areas in frontal and parietal cortex that includes the frontal eye fields (FEF) and the lateral intraparietal area (LIP) in the monkey and functionally similar areas in the human. In monkeys, physiology studies have begun to characterize the interactions across the network by simultaneously recording from two or more interconnected nodes of the attention network. One important result of these studies suggests that the strength of attentional modulation is linked to the strength of neural synchrony between areas. In contrast, in humans, little is known about the temporal dynamics and functional interactions across areas of the attention network. Further, despite the macaque brain serving as the prime model for our basic understanding of human brain function, it remains unclear how neural mechanisms related to perception and cognition compare across primate species. Another major objective in the laboratory is to characterize the temporal dynamics of the attention network in human ECoG patients and compare electrophysiological signals related to spatial attention across primate species.


Attentional selection from natural scenes

One of the great challenges of cognitive neuroscience is to reveal the neural mechanisms underlying perceptual and cognitive processes that are utilized under naturalistic conditions. Selecting a complex object from a cluttered environment (i.e. a natural scene) presents a particularly complicated problem, since the exact location of the object is often unknown, and an object has an almost infinite number of visual appearances (due, e.g., to variations in size and orientation). Despite these challenges, the visual system has an extraordinary capability to extract categorical information (e.g. detecting people or cars) quickly and efficiently from natural scenes, yet little is known about the neural mechanisms related to such real-world search. Recent studies from our laboratory have identified a category-specific biasing mechanism that operates in parallel across the visual field and enhances processing of objects that belong to the task-relevant category. Characterizing this biasing mechanism during real-world search of natural scenes is another major objective in the lab. We employ a multi-modal methods approach (i.e., psychophysics, fMRI, TMS, and ECoG recordings) with virtually identical experimental designs across approaches and subject populations.


Neuromodulation in the attention network

Cholinergic and dopaminergic systems are widely accepted to play a functional role in selective attention, but little is known about the specific effects that this modulation has on neural responses and on behavior. Acetylcholine (ACh) is the primary neuromodulator in the pulvinar nucleus of the thalamus\ which is a critical node in the attention control network. For example, our recent studies have demonstrated that the pulvinar synchronizes areas of visual cortex according to behavioral demands. We hypothesize that ACh plays an important role in the pulvinar-mediated control of attentional responses in cortex. Our laboratory is probing the effects of cholinergic modulation in the pulvinar on visual cortical responses linking ACh-dependent neural changes in visual cortex with behavior in an effort to define a causal role of the pulvinar in cognitive processing.
 
   

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Princeton University